MAX1470_02 Datasheet, PDF (3/6 Pages) Maxim Integrated Products – MAX1470 Evaluation Kit

MAX1470 Evaluation Kit
4) Turn on the DC supply. The supply current should
read approximately 6mA.
5) Activate the RF generator’s output without modula-
tion. The scope should display a DC voltage that
varies from approximately 1.2V to 2.0V as the RF
generator amplitude is changed from -115dBm to
-50dBm.
6) Set the RF generator to -100dBm. Activate the RF
generator’s modulation and set the scope’s cou-
pling to AC. The scope now displays a lowpass-fil-
tered square wave at TP3 (filtered analog base-
band data). Use the RF generator’s LF OUTPUT
(modulation output) to trigger the oscilloscope.
7) Monitor the DATA_OUT terminal and verify the pres-
ence of a 2kHz square wave.
Additional Evaluation
1) With the modulation still set to AM, observe the
effect of reducing the RF generator’s amplitude on
the DATA_OUT terminal output. The error in this
sliced digital signal increases with reduced RF sig-
nal level. The sensitivity is usually defined as the
point at which the error in interpreting the data (by
the following embedded circuitry) increases
beyond a set limit (BER test).
2) With the above settings, a 315MHz-tuned EV kit
should display a sensitivity of about -118dBm (1%
BER), while a 433.92MHz kit displays a sensitivity of
about -114dBm (1% BER). Note: The above sensi-
tivity values are given in terms of average carrier
power. If true pulse modulation is used instead of
AM, then the sensitivity measurement is in terms of
peak power, and as a result is reduced by 6dB.
3) Use capacitors C5 and C6 to set the corner fre-
quency of the 2nd-order lowpass Sallen-Key data
filter. The current values were selected for a corner
frequency of 5kHz. Adjusting these values accom-
modates higher data rates (refer to the MAX1470
data sheet for more details).
Layout Issues
A properly designed PC board is an essential part of
any RF/microwave circuit. On high-frequency inputs
and outputs, use controlled-impedance lines and keep
them as short as possible to minimize losses and radia-
tion. At high frequencies, trace lengths that are approx-
imately 1/20 the wavelength or longer become anten-
nas. For example, a 2in trace at 315MHz can act as an
antenna.
Keeping the traces short also reduces parasitic induc-
tance. Generally, 1in of a PC board trace adds about
20nH of parasitic inductance. The parasitic inductance
can have a dramatic effect on the effective inductance.
For example, a 0.5in trace connecting a 100nH induc-
tor adds an extra 10nH of inductance, or 10%.
To reduce the parasitic inductance, use wider traces
and a solid ground or power plane below the signal
traces. Using a solid ground plane can reduce the par-
asitic inductance from approximately 20nH/in to 7nH/in.
Also, use low-inductance connections to ground on all
GND pins, and place decoupling capacitors close to all
VDD connections.
The EV kit PC board can serve as a reference design for
laying out a board using the MAX1470. All required com-
ponents have been enclosed in a 1.25in x 1.25in square,
which can be directly “inserted” in the application circuit.
Table 1. Jumper Function Table
JUMPER
JU1
JU1
JU1
JU3
JU3
JU3
JU4
STATE
1-2
2-3
N.C.
1-2
2-3
N.C.
1-2
FUNCTION
Normal operation
Power-down mode
External power-down
control
Mixer output to
MIX_OUT
External IF input
Normal operation
Uses PDOUT for faster
receiver startup
JU4
2-3
GND connection for
peak detector filter
Table 2. Test Points
TP
DESCRIPTION
PLL control voltage (Note: Connecting anything to
1
this test point degrades RF performance.)
2
Data slicer negative input
3
Data slicer positive input
4
Peak detector out
5
VDD
6
GND
7
Data filter feedback node
8
Data out
9
Power-down select input
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